The present invention relates to a continuous scanning lens antenna device, and more exactly to a method and a device providing control of the direction of a main lobe or lobes of a scanning antenna without mechanically moving the antenna.
Sometimes it is desirable to be able to quickly change radiation direction of an antenna. In other words the antenna lobe is to be quickly shifted or swept between different directions. The demand regarding time is often such that an arrangement for mechanical motions of the antenna is not feasible.
Today antenna arrays are used which contain elements in which a signal phase at each element may be individually set to achieve a control of the main direction of the antenna lobe. Another technique to achieve a control of a radiation lobe is to utilize what is normally referred to as an xe2x80x9coptical phased arrayxe2x80x9d, which includes an adaptable lens which, for instance, is disclosed in a document U.S. Pat. No. 5,212,583. This document describes a device utilizing a single plate of a material presenting ferroelectric properties. In a second embodiment disclosed the ferroelectric plate is provided with a ground-plane on one side and two orthogonal grids on the other side for radiation lobe control. Both the grids and the ground-plane are made in a light transparent material, indium/tin oxide. This document only refers to optical systems and does not discuss whether this is applicable to the microwave range.
However, in a microwave system, when the wavelength of an electro-magnetic wave generally is much larger than the distance between conducting grid wires, it should be noted that only a grid wire direction-being perpendicular to the E-field vector of the propagating wave can be utilized for controlling the refractive index of the ferroelectric plate. A grid wire direction parallel to the E field vector will result in a reflection of the electromagnetic wave. In the disclosed optical system the grid conductor wire distances are expected to be much larger than the wavelength of the light, i.e. xcex less than  less than wire separation. Besides a conducting ground-plane will totally reflect the propagating microwave.
Two documents U.S. Pat. Nos. 4,706,094 and 4,636,799 both disclose a ferroelectric block between grids of parallel wires. According to the first document only controlling fields are used across the block, i.e. in the propagation direction of the wave. According to the other document the voltages at the wires are arranged such that the field may adopt arbitrary directions in the plane perpendicular to the wires. In the first document it is pointed out that the xe2x80x9cnormallyxe2x80x9d high conductive wires only transmits perpendicular, linear polarization but that they may be replaced by resistive wires being able to transmit also parallel polarization at some loss.
WO,A1,93/10571 demonstrates a development of U.S. Pat. No. 4,636,799 where only fields perpendicular to the wires are used. Here only one layer of wires is needed and the ferroelectric material has been divided into a plurality of blocks such that the grid of wires can be disposed in the middle of the ferroelectric layer.
However it will be noted that, the documents cited above are addressing the use of highly conductive wires and a voltage gradient is then achieved by applying different voltages to the individual wires according to a given pattern. Furthermore the devices described are related to utilizing the ferroelectric material for xe2x80x9celectro-optic lensesxe2x80x9d which primarily directs the utilization to frequencies corresponding to electromagnetic radiation in the nanometer range.
Furthermore none of the documents has disclosed a device being able to scan microwave radiation in two orthogonal planes in a single ferroelectric plate. Neither it has been shown that this can be done by using several layers of ferroelectric material without large losses.
Therefore there is still a demand for a method and a device, which will operate even at a much lower frequency range, i.e., in the microwave range.
The present invention discloses a method and a device for the generation of a lens device including a plate of ferroelectric material, the transmission phase gradient of which is varied over the surface of the lens by means of controllable static electric fields. The lens may involve an entire antenna aperture, e.g. a feeder horn or constitute a surface covering a slotted waveguide antenna, be a portion of a microwave antenna aperture or an element in a conventional microwave array aperture. The division of the aperture depends on the number of degrees of freedom to be controlled simultaneously. In a general case N lobes and M nulls are to be controlled at the same time. In the most simple case with N=1 and M=0 the lens will cover the entire antenna aperture.
According to the present invention an electromagnetically transparent highly resistive film is applied at both sides of a plate presenting ferroelectric properties. At two opposite edges of these resistive films highly conducting wires are applied and electrically connected along the resistive film. The pairs of highly conductive wires at the opposite edges of each one of the two films on the plate presenting the ferroelectric properties are running perpendicular to each other. The first pair of highly conducting wires parallel to the y-axis is connected to a variable voltage source (Ux), while the second pair of highly conducting wires parallel to the x-axis is connected to a second variable voltage source (Uy). In this way a lobe may be steered in the X-Z plane by Ux and in the Y-Z plane by Uy. In order to obtain low losses and no change of the controlling E field polarity when sweeping the voltage sources, a bias source of the order several hundreds of volts is applied between the two voltage sources. Another benefit of the present design is that it will operate independent of the polarization of the passing microwave power.
A method according to the present invention is set forth by the attached independent claim 1 and by the dependent claims 2 to 3.
Similarly a continuous scanning lens antenna device according to the method of the present invention is set forth by the attached independent claim 4 and further embodiments are defined in the dependent claims 5 to 6.